The present invention relates to positive displacement hydraulic pumps of the roller vane type, and more particularly, to an improved rotor configuration which provides reduced pressure pulses.
Pumps of the type to which the present invention relates include a housing defining a pumping chamber, and a pumping element rotatably disposed in the pumping chamber and defining expanding and contracting fluid chambers. The housing means defines a fluid inlet port in communication with the expanding fluid chambers, and a fluid outlet port in communication with the contracting fluid chambers. The pumping element includes a rotor member mounted for rotation with an input shaft, the rotor member having a plurality of slots. Each of the slots receives a radially displaceable roller vane member. The pumping chamber is defined by a continuous arcuate wall surface including an inlet arc surface of progressively increasing radius in the direction of rotation of the rotor member, and a discharge arc surface of progressively decreasing radius.
Although the present invention could be utilized with various types of roller vane pumps, it is especially advantageous when used with a balanced roller vane pump, i.e., a pump in which there are two oppositely disposed expanding fluid chambers, and two oppositely disposed contracting fluid chambers. The term "balanced" derives from the fact that the arrangement of fluid chambers results in balanced hydraulic forces acting on the rotor member.
One of the reasons for the present invention being especially advantageous for use in balanced pumps is that a balanced pump is more likely to utilize what will be referred to hereinafter as a "high displacement" cam surface for the discharge arc surfaces. Although the term "high displacement" cam surface will be described in greater detail in the subsequent specification, it will be understood by those skilled in the art that the term does not define or refer to any particular cam surface geometry, but instead, refers to the fact that the discharge arc surface must accomplish the full radially inward displacement of the roller vane over a relatively small angular displacement of the rotor member.
One of the primary problems associated with pumps of the type described is the generation of undesirable pressure pulses during the pumping cycle. Such pulses may be transmitted through the hydraulic lines to other components such as the vehicle steering gear and steering column which can then translate the pressure pulses into noise, audible to the driver. Pressure pulses and noise emanating from the pump can be generated in several ways, and it has long been an object of those skilled in the art to identify and eliminate such sources of noise and pressure pulses.
Accordingly, it is a primary object of the present invention to identify and eliminate additional sources of pressure pulses and noise which have been previously unrecognized.
Those skilled in the art have for a long time recognized that one of the potential causes of pressure pulses is intermittent leakage of fluid from a contracting fluid chamber, past one of the roller vanes, to an expanding fluid chamber. It has also been recognized by those skilled in the art that one likely cause of such intermittent leakage is radial movement of the roller vane, into and out of engagement with the discharge arc surface as the roller vane moves through the pumping (discharge) arc. It has generally been assumed that such movement or bouncing of the roller vane could be prevented by exerting greater net radially outward force on the roller vane to keep it in contact with the discharge arc surface.
Accordingly, it is another object of the present invention to identify and reduce substantially the causes of the roller vane bouncing and the resultant intermittent leakage.
The above and other objects of the present invention are accomplished by the provision of an improved rotary pump of the type described above wherein each of the discharge arc surfaces comprises a high displacement cam surface. Each of the slots includes a drive surface disposed to engage and drive the adjacent one of the roller vane members when the pumping element is operating in the pumping mode. Each of the slots also includes an opposite surface. Each of the driving surfaces includes a substantial surface portion oriented at a negative angle relative to a radial line passing through the axis of rotation of the pump, and through the center of the adjacent roller vane member. The engagement of each of the roller vane members and its respective negative surface portion acts on the roller vane member in a direction to reduce the net radially outward force, and is effective to reduce the radial movement of the roller vane member into and out of engagement with the adjacent discharge arc surface.